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    <script type="text/javascript">
        AO={n=undefined , o=undefined}
        function fun(n,o){
            console.log(o);
            return{
                fun:function(m){
                    return fun(m,n);
                }
            }
        }
        下面每一行的输出分别是什么
        var a = fun(0);a.fun(1);a.fun(2);a.fun(3);
        //undefined,0,0,0

        var b = fun(0).fun(1).fun(2).fun(3);
        //undefined,0,1,2
        
        var c = fun(0).fun(1);c.fun(2);c.fun(3);
        //undefined,1,0,1
// ////////////////////////////////////////////////

        function fn(a){
            this.a = a
        }
        var obj={}
        var getNum = fn.bind(obj);
        getNum(2);//2
        console.log(obj.a);

//  ///////////////////////////////////////////


//使用递归求到20的斐波那契数列之和
        //看网上的
        function fn(n){
              if (n<0) {
                  return 'N的值不能小于0'
                  
                  
              }else if(n==0||n==1){
                  return 1;         

              }
              else if (n >1){
                  return fn(n-1)+fn(n-2)
              }
          }
          console.log(fn(20));


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